1. Field of the Invention
The present invention relates to a system for controlling the opening and closing operation of a car door of an elevator or lift, the system being capable of eliminating danger of a passenger being caught in the door.
2. Description of the Related Art
FIG. 4 illustrates the mechanical construction of an elevator door system of the type disclosed in Japanese Patent Laid-Open No. 1-231794. Referring to this figure, the door system has a car door 3 provided on an entrance 2 of a car 1, a hanger case 4 provided on the top of the car 1, a rail 5 fixed to the hanger case 4, a door hanger 6 fixed to the upper end of the car door 3, and rollers 7, 8 provided on the top of the door hanger 6 and adapted for rolling along the upper and lower surfaces of the rail 5. Numeral 9 denotes an engaging device mounted on the door 3. When the car 1 is stopped in a door zone, the engaging device 9 engages with a device (not shown) provided on a landing door so as to link the car door 3 and the landing door. Numeral 10 denotes a driving unit mounted on the hanger case 4 and including an electric motor 11. The driving unit 10 is drivingly connected through a 4-link type connecting mechanism 12. The electric motor 11 is driven through an inverter 13.
FIG. 5 is a block diagram of a control system for controlling a door system having the above-described construction. Referring to this figure, the control system includes a converter 21 for rectifying three-phase A.C. power of R, S and T phases, a smoothing capacitor 22 for smoothing the output of the converter 21, and an inverter 23 for receiving the smoothed output from the smoothing capacitor 22. The inverter 23 includes switching devices such as transistors, field effect transistors or the like, and is capable of converting the D.C. voltage supplied thereto into a three-phase A.C. voltage which is supplied to the electric motor 11. The switching devices receive a PWM pulse from a PWM unit 38 so as to effect pulse width modulation of the output.
The operation speed and the torque of the electric motor 11 are thus controlled by the power supplied through the inverter 23. The driving unit 10, with the controlled speed and torque, drives the car door 3 through the link mechanism 12, so that the car door 3 moves with its rollers 7, 8 rolling along the rail 5, thereby opening and closing the entrance 2.
An encoder 24 directly coupled to the electric motor 11 produces a pulse train .omega..sub.rp * including pulses the number of which corresponds to the angle of rotation of the rotor of the electric motor 11. The pulse train .omega..sub.rp * is input to a speed detector 25 which counts the number of pulses per unit time, thus computing the motor speed .omega..sub.r *. Numeral 26 designates a speed command generator which generates a speed command .omega..sub.r for commanding the speed of the electric motor 11. The speed command .omega..sub.r and the speed .omega..sub.r * are added together in an adder 27 so that a speed offset .DELTA..omega..sub.r is obtained. The speed offset .DELTA..omega..sub.r is input to a speed amplifier 28 which generates, for example, a torque command in the form of a torque current command iq necessary for enabling the electric motor 11 to operate at the command speed .omega..sub.r. The torque current command iq is delivered to a slip computing unit 29, together with an exciting current command id which is constant when the torque is constant. The slip computing unit 29 then computes a slip frequency in accordance with the following formula: EQU .omega..sub.s =(L.sub.2 R.sub.2).multidot.(iq/id)
where L.sub.2 represents the secondary reactance of the electric motor 11 (calculated on the basis of the primary side and R.sub.2 represents the secondary resistance of the electric motor (calculated on the basis of the primary side).
The slip frequency .omega..sub.s and the pulse train .omega..sub.rp * are added together by an adder 30, the output of which is delivered to a phase counter 31 which forms an integrator. The phase counter 31 then computes the angle .theta..sub.r of rotation of the electric motor 11 in accordance with the following formula. EQU .theta..sub.r =.intg.(.omega..sub.rp *.+-..omega..sub.s)dt
On the other hand, the torque current command iq and the exciting current command id are supplied to a phase angle computing unit 32 which determines the phase angle .theta..sub.i in accordance with the following formula. EQU .theta..sub.i =tan.sup.-1 (iq/id)
The phase angle .theta..sub.i and the rotation angle .theta..sub.r are added together by an adder 33 so that the actual current phase angle .theta. is determined as .theta.=.theta..sub.i +.theta..sub.r.
The torque current command iq and the exciting current command id are input to a current amplitude computer 34 which determines the current amplitude .vertline.I.vertline. in accordance with the following formula. EQU .vertline.I.vertline.=.sqroot.id.sup.2 +iq.sup.2
The current amplitude .vertline.I.vertline. and the actual current phase angle .theta. are input to a current command generator 35 which produces a U-phase current command IU and a V-phase current command IV as follows: EQU IU=.vertline.I.vertline..multidot.sin .theta. EQU IV=.vertline.I.vertline..multidot.sin (.theta.+2.pi./3)
On the other hand, the currents in the U- and V-phase of the electric motor 11 are detected by a DC current transformer 37 as actual motor currents IU* and IV*. The actual motor currents IU* and IV* and the current commands IU and IV are input to a current amplifier 36 which computes offset values .DELTA.IU and .DELTA.IV, as well as .DELTA.IW=-.DELTA.IU-.DELTA.IV, which are supplied to the PWM unit 38. The PWM unit 38 then computes a 3-phase PWM voltage command corresponding to the above-mentioned offsets as a change-over signal C which is delivered to the inverter 23. The inverter 23 then operates the switching device in accordance with the pulse train included in the change-over signal C, so as to control the currents, voltage and frequency of the power supplied to the electric motor 11, whereby the speed and the torque of the electric motor 11 are controlled.
Numeral 39 designates a position counter for counting the pulses of the pulse train .omega..sub.rp * from the encoder 24 so as to detect the position of the car door 3, While numeral 40 designates an accident detector for detecting a passenger caught by the car door 3 upon receipt of the signals from the position counter 39 and the speed detector 25 and for producing a reversing instruction 40a.
During closing of the car door 3, the speed .omega..sub.r * varies in relation to time in a manner shown in FIG. 6. In this Figure, t.sub.1 and t.sub.2 represent, respectively, the moment at which closing is commenced and the moment at which closing is ceased.
When a passenger is caught by the car door 3 during closing, the car door 3 is decelerated so that the speed .omega..sub.r * of the motor is reduced. As this speed comes down below a predetermined speed .omega..sub.d, the above-mentioned reversing instruction 40a is given to reverse the car door 3. Thus, the accident detector 40 produces the reversing instruction 40a so as to reverse the car door 3 to ensure safety when the car door position 3 detected from the output of the position counter 39 is within a region AB and it is detected that the motor speed .theta..sub.r * is below the predetermined speed .omega..sub.d.
In the known elevator door control system having the above-described construction, the reversing instruction 40a is generated when it is detected that the speed .omega..sub.r * of the door driving motor 11 has come down below the predetermined speed .omega..sub.d. However, as can be seen from FIG. 6, an obstruction of the car door is materially undetectable outside the region AB, since the speed .omega..sub.r * of the door driving motor 11 is already low.